In recent years, higher integration and miniaturization of semiconductors widely used in electronic equipment, communication instruments, personal computers, and the like have accelerated increasingly. With this, various characteristics required of laminates for semiconductor packages used in printed wiring boards have become increasingly strict. Examples of the required characteristics include characteristics such as low water absorbency, heat resistance after moisture absorption, flame retardancy, a low dielectric constant, a low dielectric loss tangent, a low thermal expansion coefficient, heat resistance, and chemical resistance. But, these required characteristics have not always been satisfied so far.
Conventionally, as resins for printed wiring boards having excellent heat resistance and electrical characteristics, cyanate compounds are known, and a resin composition using a bisphenol A-based cyanate compound and another thermosetting resin and the like is widely used for printed wiring board materials and the like. The bisphenol A-based cyanate compound has characteristics excellent in electrical characteristics, mechanical characteristics, chemical resistance, and the like but may be insufficient in low water absorbency, heat resistance after moisture absorption, and flame retardancy, and therefore for the purpose of further improving characteristics, various cyanate compounds having different structures are studied.
As a resin having a structure different from the bisphenol A-based cyanate compound, a novolac-based cyanate compound is often used (for example, see Patent Literature 1), but there are problems such as the novolac-based cyanate compound being likely to be insufficiently cured, and the water absorption rate of the obtained cured product being high and the heat resistance after moisture absorption decreasing. As a method for improving these problems, prepolymerization of a novolac-based cyanate compound and a bisphenol A-based cyanate compound is proposed (for example, see Patent Literature 2).
In addition, as a method for improving flame retardancy, a halogen-based compound being contained in a resin composition by using a fluorinated cyanate compound or mixing or prepolymerizing a cyanate compound and a halogen-based compound is proposed (for example, see Patent Literatures 3 and 4).